Tunnel Magnetoresistance Effect for Ni₈₀Fe₂₀/Co/N(N=Ta, Cu, Al)/Al-oxide/Co Junctions

Abstract

The effect on the tunneling magnetoresistance (TMR) of inserting the nonmagnetic metals (NMs) Al, Cu, and Ta between the insulator and ferromagnetic layer of a tunnel junctions was investigated. The TMR ratio for a junction with Ta decreased rapidly with increasing Ta thickness, while that for a junction with Al remained more than 50 Å of the thickness. From cross-sectional TEM and AFM measurement, it was found that a junction with thick Al has an insulating layer on both sides of the metallic Al; that is, it would be a double-barrier tunnel junction. We compared the experimental result for the metallic Al thickness dependence of the TMR ratio with the theory of double tunnel junctions. Consequently, the spin diffusion length of Al was estimated to be sub-micrometer.